From Laos, U.S. President Barack Obama denounced Donald Trump as unfit to be the American commander-in-chief, after the Republican presidential candidate said Russian President Vladimir Putin has been more of a leader than Obama.

"I do not think the guy's qualified to be president of the United States and every time he speaks, that opinion is confirmed," Obama said in what was an unusually caustic comment about the U.S. presidential contest while he was traveling overseas.

Late Wednesday, Trump said at a nationally televised candidate forum that Putin was "far more than our president has been a leader" and that U.S. military generals have been "reduced to rubble" under Obama.

Obama, at the end of his last presidential trip to Asia, said as president, "You actually have to know what you are talking about and you actually have to have done your homework. When you speak, it should actually reflect thought out policy you can implement."

Obama, who staunchly supports Trump's Democratic candidate, former Secretary of State Hillary Clinton, said, "The most important thing for the public and the press is to just listen to what he says and follow up and ask questions to what appear to be either contradictory or uninformed or outright wacky ideas."

'Very good relationship' with Putin

During an NBC News forum Wednesday in which Trump was interviewed separately from Clinton, Trump said he thinks if he is elected and succeeds Obama as president, he would have a "very good relationship with Putin." He said Russia and the United States have a joint interest in defeating Islamic State jihadists.

"Russia wants to defeat ISIS as badly as we do," he said. "If we had a relationship with Russia, wouldn't it be wonderful if we could work on it together and knock the hell out of ISIS?"

He further criticized U.S. military action in Iraq under Obama, saying generals "have not been successful." Trump repeated his assertion the United States should have seized oil from Iraq.

"If we would have taken the oil, you wouldn't have ISIS, because ISIS formed with the power and wealth of that oil," Trump contended.

Intelligence briefing

As a major party candidate, Trump has received confidential intelligence briefings meant to ensure that the next leader is knowledgeable about U.S. foreign policies when their term begins. When asked if he was shocked by anything he heard, Trump said Obama, Clinton and Secretary of State John Kerry did the opposite of what intelligence experts told them.

"I am very good with body language. I could tell they were not happy our leaders did not follow what they were recommending," he said.

Trump said he was qualified to be commander-in-chief because “I built a great company; I’ve been all over the world; I’ve dealt with foreign countries... I have great judgment; I know what’s going on.”

Trump also said he was "totally against the war in Iraq," a claim that is contradicted by his initial support for the 2003 U.S. invasion.

Clinton said that her vote for the Iraq war when she was a U.S. senator was a mistake, but that it was important to learn from mistakes. She also pushed back against Trump's repeated assertions during the campaign that he opposed the U.S. attack on Iraq.

"He supported it before it happened, he supported it as it was happening, and he is on the record as supporting it after it happened," Clinton said. "I have taken responsibility for my decision. He refuses to take responsibility for his support. That is a judgment issue."

Clinton said the most important quality in a president is steadiness and the strength to make hard decisions.

"What you want in a president, a commander-in-chief, is someone who listens, who evaluates what is being told to him or her, who is able to sort out the very difficult options being presented, and then makes the decision," she said.

Emails, counterterrorism

She has faced criticism and investigations for her use of an unsecured private email server while serving as the country's top diplomat during Obama's first term, from 2009 to 2013. Investigators said she was "extremely careless," but criminal charges were not warranted.

"It was something that should not have been done," she said, adding that there was no evidence her system was hacked.

Clinton called the fight against Islamic State the top counterterrorism goal, advocating using air power and getting more support from Arabs and Kurds fighting IS militants, while also supporting the Iraqi military. She said no U.S. ground combat troops would go to Iraq or Syria.

"I view force as a last resort, not a first choice," she said.

Trump and Clinton will square off directly in their first presidential debate on September 26, with two more scheduled in October in the weeks before the November 8 election.